I am working on ASP.NET sample projects in Microsoft Visual Studio Community 2017. The project I am currently working on was running fine yesterday. When I opened the project today, I immediately receive a message box:
The project system has encountered an error.
An element with the same key but different value already exists. Key: Microsoft.EntityFrameworkCore.InMemory
A diagnostic log has been written:
=====================
Crippling
System.AggregateException: One or more errors occurred. ---> System.ArgumentException: An element with the same key but a different value already exists. Key: Microsoft.EntityFrameworkCore.InMemory
at System.Collections.Immutable.ImmutableDictionary`2.HashBucket.Add(TKey key, TValue value, IEqualityComparer`1 keyOnlyComparer, IEqualityComparer`1 valueComparer, KeyCollisionBehavior behavior, OperationResult& result)
at System.Collections.Immutable.ImmutableDictionary`2.AddRange(IEnumerable`1 items, MutationInput origin, KeyCollisionBehavior collisionBehavior)
at System.Collections.Immutable.ImmutableDictionary`2.AddRange(IEnumerable`1 pairs, Boolean avoidToHashMap)
at System.Collections.Immutable.ImmutableDictionary`2.AddRange(IEnumerable`1 pairs)
at Microsoft.VisualStudio.ProjectSystem.Designers.ProjectBuildSubscriptionService.UpdateRuleSnapshotCore(IProjectVersionedValue`1 source, String ruleName, IRule rule, ImmutableDictionary`2 items, ImmutableDictionary`2 properties, ImmutableList`1 recentItemRenames, IProjectChangeDiff& diff)
at Microsoft.VisualStudio.ProjectSystem.Designers.ProjectRuleSubscriptionServiceBase`1.UpdateSnapshotCoreAsync(TSource source, IImmutableSet`1 subscribedElements, IProjectVersionedValue`1 previousResult)
at Microsoft.VisualStudio.ProjectSystem.Designers.CustomizableBlockSubscriberBase`3.<UpdateSnapshotAsync>d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.Designers.CustomizableBlockSubscriberBase`3.<>c__DisplayClass27_0.<<Initialize>b__1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask.<JoinAsync>d__76.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask`1.<JoinAsync>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.Designers.CustomizableBlockSubscriberBase`3.<<Initialize>b__27_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.DataflowExtensions.<>c__DisplayClass23_0`2.<<CreateSelfFilteringTransformBlock>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.VisualStudio.ProjectSystem.CommonProjectSystemTools.Rethrow(Exception ex)
at Microsoft.VisualStudio.ProjectSystem.ProjectErrorReporting.<>c__DisplayClass6_0.<SubmitErrorReport>b__0()
at Microsoft.VisualStudio.ProjectSystem.ExceptionFilter.<>c__DisplayClass2_0.<Guard>b__0()
at GuardMethodClass.GuardMethod(Func`1 , Func`2 , Func`2 )
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.ArgumentException: An element with the same key but a different value already exists. Key: Microsoft.EntityFrameworkCore.InMemory
at System.Collections.Immutable.ImmutableDictionary`2.HashBucket.Add(TKey key, TValue value, IEqualityComparer`1 keyOnlyComparer, IEqualityComparer`1 valueComparer, KeyCollisionBehavior behavior, OperationResult& result)
at System.Collections.Immutable.ImmutableDictionary`2.AddRange(IEnumerable`1 items, MutationInput origin, KeyCollisionBehavior collisionBehavior)
at System.Collections.Immutable.ImmutableDictionary`2.AddRange(IEnumerable`1 pairs, Boolean avoidToHashMap)
at System.Collections.Immutable.ImmutableDictionary`2.AddRange(IEnumerable`1 pairs)
at Microsoft.VisualStudio.ProjectSystem.Designers.ProjectBuildSubscriptionService.UpdateRuleSnapshotCore(IProjectVersionedValue`1 source, String ruleName, IRule rule, ImmutableDictionary`2 items, ImmutableDictionary`2 properties, ImmutableList`1 recentItemRenames, IProjectChangeDiff& diff)
at Microsoft.VisualStudio.ProjectSystem.Designers.ProjectRuleSubscriptionServiceBase`1.UpdateSnapshotCoreAsync(TSource source, IImmutableSet`1 subscribedElements, IProjectVersionedValue`1 previousResult)
at Microsoft.VisualStudio.ProjectSystem.Designers.CustomizableBlockSubscriberBase`3.<UpdateSnapshotAsync>d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.Designers.CustomizableBlockSubscriberBase`3.<>c__DisplayClass27_0.<<Initialize>b__1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask.<JoinAsync>d__76.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask`1.<JoinAsync>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.Designers.CustomizableBlockSubscriberBase`3.<<Initialize>b__27_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.DataflowExtensions.<>c__DisplayClass23_0`2.<<CreateSelfFilteringTransformBlock>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.VisualStudio.ProjectSystem.CommonProjectSystemTools.Rethrow(Exception ex)
at Microsoft.VisualStudio.ProjectSystem.ProjectErrorReporting.<>c__DisplayClass6_0.<SubmitErrorReport>b__0()
at Microsoft.VisualStudio.ProjectSystem.ExceptionFilter.<>c__DisplayClass2_0.<Guard>b__0()
at GuardMethodClass.GuardMethod(Func`1 , Func`2 , Func`2 )<---
===================
It also caused some other problems such as all of my using directives for the System and Microsoft namespaces giving errors:
The type or namespace name 'System' could be found (are you missing a using directive or an assembly reference?)
Since these directives are still working fine for other projects, I suspect they will subside when the EntityFramework problem is fixed.
I have tried restarting both Visual Studio and my computer and have tried building the project anyway. I am not able to add references to the project. I receive message boxes:
A task was canceled
The operation could not be completed
References to namespaces within the project are still working fine.
Thank you for your help.
Close VS.
Open your project file (csproj file or project.json) via
an external text editor and remove duplicated package references.
Reopen VS. All should work fine.
If a csproj file format is used - look for the lines like this:
<PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="1.1.1" />